python whois Socket Error: [Errno -2] Name or service not known

Question

After trying to get whois info via whois python package:

import whois

w = whois.whois(url)

For some urls I get error:

Socket Error: [Errno -2] Name or service not known

What is the meaning of this error?

Also in some cases I get Socket Error: [Errno 104] Connection reset by peer error.

My setting:

pip freeze | grep whois
python-whois==0.6.7
pythonwhois==2.4.3
whois==0.7

Python 3.6.2 |Anaconda custom (64-bit)| (default, Sep 30 2017, 18:42:57) 
[GCC 7.2.0] on linux